CEREAL growers in the UK will be on 'Red' alert this year as it has been confirmed that the yellow rust isolate, Red 24, is now firmly established in the UK wheat population – and its potency means that it is 'not welcome news'.

This group of isolates was first known to be present in the UK in 2016 and it probably played a key role in unexpected disease levels and revision of disease ratings in that year, according to experts from AHDB.

Recent tests on yellow rust isolates present in crops in 2017 have revealed that it is now the most dominant group in the UK yellow rust population. The findings were presented at the annual UK Cereal Pathogen Virulence Survey (UKCPVS) stakeholder event, which took place last week in Cambridgeshire.

However, despite the prevalence of Red 24's influence, compared with 2016, yellow rust levels were generally lower in 2017 and disease observations much more in line with the disease ratings presented in the AHDB Recommended Lists.

Dr Sarah Holdgate, UKCPVS project manager, who is based at NIAB, said: “Autumn, 2016, was quite dry, and cold snaps last spring seemed to have dampened the disease going into the summer. We’ve also only received two yellow rust samples so far this year, most likely due to the cold weather this winter.”

In total, 114 wheat yellow rust samples were received by UKCPVS in 2017, compared to 340 samples received in 2016. Tests on 2017 samples, though, revealed the continued dominance of Red group.

Its isolates were the most commonly found (36% frequency), followed by Red 28 (29% frequency) and Red 11 (14% frequency). The pink and purple groups were not detected in 2017 and beyond the dominant red group, only blue-group isolates were detected in 2017.

This, however, did not include the Blue 7 group which, like Red 24, was one of the causal groups of isolates behind the 2016 epidemic.

Dr Holdgate added: “Work is underway to establish if Red 24 isolates are outcompeting other isolates. It’s important to understand the make-up of the yellow rust population to understand the impact on varieties. For example, Red 24 is relatively damaging compared to other isolates and its continued presence in the UK is not welcome news.”

Several new pathotypes from the already highly diverse Red groups were also identified in 2017 (Red 27 to Red 30), in addition to another pathotype which has yet to be assigned to a group.

Red 30 is similar to the PstS14 isolates detected elsewhere in Europe. This was first detected in Morocco and Sicily in 2016 and caused widespread disease epidemics in Morocco in 2017.

At this stage, the potential impact of this new pathotype on UK wheat varieties is unknown. Adult plant trials have been set up to help quantify the risk.

Meanwhile, the monitoring programme reported that brown rust in wheat appeared relatively late in 2017, with high levels of the disease observed in crops from June.

No unexpected disease, however, was reported to UKCPVS, though isolates have become more complex in recent years and the latest seedling tests found 26 different pathotypes in the 27 isolates tested.

Also reported was that mildew pressures were relatively high in 2017. For wheat, powdery mildew saw an increase in virulence for most resistance genes but there were no significant reports of any resistance breakdown in the field.

For barley producers, powdery mildew's virulence frequencies were generally stable, although some increased, whereas others decreased. Once again, UKCPVS received no reports of unexpected disease in crops.

* A new four-year EU-funded project called ‘Rustwatch’ was announced at the event. Led by the Global Rust Reference Centre, in Denmark, this will monitor rusts across Europe and develop a co-ordinated early warning system. As part of it, people are being asked to extend their monitoring and sampling beyond cereal crops to include the alternative host – common barberry.

How to send disease samples:

The UKCPVS is always checking for new races of cereal rusts and mildews across the UK and relies on samples being sent in from the field.

It is asking for samples of infected leaves showing signs of wheat yellow rust, brown rust and powdery mildew as well as barley powdery mildew to be sent to it as part of the monitoring process. These infected leaves will give the team at NIAB the isolates needed to conduct the survey to identify any possible changes in the race of the diseases.

The majority of samples are expected in May, June and July – the peak of the rust and mildew season – but it receives some in the autumn when conditions have been mild enough for the disease to carry on.

"Samples can be from any variety, but we are especially interested in varieties which are noted as resistant to the different diseases at that time, said a spokesman.

Yellow/brown rust:

Samples should consist of 5-10 infected leaves and the rust should be active and fresh. Fold each leaf length-wise, upper surfaces together and wrap in slightly damp kitchen roll (or similar). Put in an envelope saying where the sample came from.

Mildew:

As with the rusts, pick 5-10 infected leaves and action as above, but this time enclose the sample in a plastic bag.

* Send samples to: FREEPOST UKCPVS